The present invention relates to a system for correcting a tone of a display such as a matrix display device.
FIG. 10 shows a conventional matrix display device.
The display device comprises a display panel 10 driven by a signal electrode driver 12 and a scanning electrode driver 14.
A video signal is applied to an A/D converter 16 in which the video signal is converted into a digital signal. The converted signal is applied to a memory 20 through a tone correcting unit 18 and stored therein. A controller 22 is provided for controlling the memory 20 and the drivers 12 and 14. The memory 20 applies a data signal to the signal electrode driver 12.
In the system, the tone correcting unit 18 is provided for directly applying gamma (.tau.) correction to the converted digital video signal. Accordingly, problems rise as follows.
(1) The effective number of luminances is extremely reduced. If the number of luminances at the input is 256, the number of luminances at the output is reduced to 183.
(2) If the input signal has a linear characteristic, a black part on the panel becomes toneless by the correction.
In the case that the analog video signal is corrected at the gamma, following problems rise.
(1) It is difficult to adjust a correcting value. PA1 (2) The signal can not be reproduced. PA1 (3) Tone changes with time. Namely, a correction curve changes.